Core Java - Interview Questions and Answers for 'Java.util' | Search Interview Question

Core Java - Interview Questions and Answers for 'Java.util' - 15 question(s) found - Order By Newest

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Q1. What is the difference between comparable and comparator in java.util pkg?

Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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Q2. What's wrong with this code ?

public static void main(String[] args) {
String regex = "(\\w+)*";
String s = "Java is a programming language.";

Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(s);
while (matcher.next()) {
System.out.println("The e-mail id is: " + matcher.group());
}
}

Core Java

Ans. matcher.find() should have been used instead of matcher.next() within while.

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Q3. What is concurrent interface ?

Core Java

Ans. ConcurrentMap is an interface and it is a member of the Java Collections Framework. It represents a Map that is capable of handling concurrent access to it without affecting the consistency of entries in a map. ConcurrentMap interface present in java.util.concurrent package.

HashMap operations are not synchronized, while Hashtable provides synchronization. Though Hashtable is thread-safe, it is not very efficient. To solve this issue, the Java Collections Framework introduced ConcurrentMap in Java 1.5.

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Q4. Which of the following is not a valid java.util.Locale initialization ?

a. new Locale ()
b. new Locale ( String language )
c. new Locale ( String language , String country )

Core Java

Ans. a i.e new Locale()

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Q5. Which of the following is not a valid NumberFormat initialization ?

a. NumberFormat.getInstance()
b. NumberFormat.getDateInstance()
c. NumberFormat.getCurrencyInstance()
d. NumberFormat.getNumberInstance()

Core Java

Ans. b i.e NumberFormat.getDateInstance()

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Q6. Which of the following code is correct ?

a. Date date = DateFormat.newInstance(DateFormat.LONG, Locale.US).parse(str);

b. Date date = DateFormat.newInstance(DateFormat.LONG, Locale.US).format(str);

c. Date date = DateFormat.getDateInstance(DateFormat.LONG, Locale.US).parse(str);

Core Java

Ans. c

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Q7. Name few Date and Time Classes you have used in your projects ?

Ans. http://www.buggybread.com/2015/02/java-util-date-time-classes-and.html

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Q8. Name few Calendar related classes and Interfaces ?

Ans. http://www.buggybread.com/2015/02/java-util-calendar-classes-and.html

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Q9. Name few Locale classes and interfaces ?

Ans. http://www.buggybread.com/2015/01/java-locale-classes-and-interfaces.html

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Q10. Name few classes that are part of java.util package ?

Ans. http://www.buggybread.com/2015/01/java-javautil-classes-and-interfaces.html

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Q11. Name few Java util classes that were introduced with Java 7 ?

Ans. http://www.buggybread.com/2015/01/migrating-to-java-7-new-classes_25.html

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Q12. Name few Java Util classes introduced with Java 8 ?

Core Java

Ans. http://www.buggybread.com/2015/01/migrating-to-java-8-new-classes_25.html

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Q13. What is the use of java.util.concurrent package in Java ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

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Q14. What are the advantages and disadvantages of using lock classes from java.util.concurrent.locks vs. synchronized methods ?

Core Java

Ans. http://www.devinline.com/2015/10/Lock-Vs-synchronized-in-java.html

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Q15. Can we load environment variables into Properties in Java ? How ?

Core Java

Ans. Yes

new Properties().putAll(System.getenv());

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